WHY CRETACEOUS PALEOCLIMATOLOGY REMAINS A MYSTERY

Our understanding of Cretaceous paleoclimatology and paleoceanography rest on analogy with the modern world, but the geologic information on conditions in the Cretaceous world comes from a sample of only about half of the planet surface that existed at that time. The half that is preserved is not representative of the planet as a whole. At present, the oceans and their marginal seas cover 71% of the planet. Deep marginal seas with restricted communication to the major basins occupy 6% of the Earth's surface, and 4% is in shallow seas and shelf regions along the continental margins. At the mid-Cretaceous sea-level high stand about 90 Ma, water covered 78% of the planet. The Panthalassa-Eastern Tethys ocean covered 51% of the planets surface. All but 10% of this area has been lost to subduction. A myriad of restricted marginal seas occupied the remaining 27% of the water-covered planetary surface, 11% as deep basins and 16% as shallow seas. The western Tethys and North Atlantic formed a subtropical seaway for surface waters, but, in contrast to the modern Southern Ocean had a highly complex bathymetry with many isolated deep basins separated by platforms. Panthalassa and the Eastern Tethys should have been a region of great paleoceanographic and climatic stability, but we will never know because that piece of the puzzle that is missing. What is left for us to study are the marginal and shelf seas, transcontinental seaways, and subcontinent-scale islands. Evaporation and precipitation differentiated the seas from one another while the ubiquitous nearby presence of water stabilized climate over land. Cretaceous marginal seas that might generate dense ocean interior waters had five times the area of their modern counterparts. It is likely that the part of the Cretaceous ocean that has been preserved was dominated by flows from both shallow and deep marginal seas, each with its own characteristics, currents, and influence on local climate.